Speaker
Description
Ag-111 is a radionuclide with prospective applications in the field of theranostics, i.e. the simultaneous imaging and treatment using a single radiopharmaceutical. It is a beta-decaying nuclide, with the emitted beta particles having suitable energies ($E_{β,mean}=$360 keV) for traversing only short distances within the tissues and interacting almost exclusively with cancer cells. Beta decay is accompanied by the emission of two relatively low energy gamma rays (245 and 342 keV) that can be utilized in the application of the Single Photon Emission Computed Tomography (SPECT) technique for diagnosis. Nevertheless, several drawbacks related to the production of the radionuclide have hindered research and development of Ag-111-labelled drugs. Neutron irradiation of palladium targets is the most common method to produce Ag-111, via the activation of naturally occurring Pd-110 nuclei and the subsequent decay of activation product Pd-111 to Ag-111. However, purity and total activity of the final product can be negatively affected due to the complexity of Ag/Pd separation and the limited natural abundance of the Pd-110 isotope.
The scope of the present work was to develop and optimize a method for the quick and efficient separation of Ag-111 from the Pd target matrix for future applications in medical research. Pd targets weighing up to 20 mg were irradiated under neutron flux (maximum 3.9E+12 $cm^{-2}$$s^{-1}$) for up to 12 h at the TRIGA MARK II research reactor of Jožef Stefan Institute, Ljubljana, Slovenia. Total Ag-111 activities and radionuclidic impurities were determined at the end of irradiation by gamma spectrometry. In our previous studies, efficient Ag/Pd separation was achieved with Ni Resin, but only batch mode was effective for larger target masses. In order to further simplify this process, dimethylglyoxime (DMG), the active component of the resin which binds Pd(II) ions, was used instead of a chromatography resin, to quickly and selectively precipitate Pd from the dissolved target. Ag-111 was then separated and isolated, and separation efficiencies and method performance was compared with the method involving Ni Resin. Finally, a recovery procedure using ascorbic acid was applied to almost quantitatively retrieve the original Pd target, for additional irradiation cycles.